1. Field of the Invention
The present invention relates to a method for determining a soil parameter using a soil compaction device that has a contact element that is charged with vibration for soil compaction.
2. Description of the Related Art
Vibrating plates and vibrating tampers, as well as vibrating rollers, are known for use as soil compaction devices. Each of these has at least one soil contact element that is charged with vibration by a vibration exciter and that introduces the vibration into the soil in order to achieve a compaction effect.
In order to monitor the quality of compaction work, it is helpful to determine particular soil parameters, such as for example soil rigidity, deformability, load capacity, etc.
In order to determine soil parameters, methods and devices are known that operate separately from soil compaction devices. Thus, there is a standardized plate load method (DIN 18134) in which a modulus of deformation Ev is determined in the context of a static load plate pressure test. Likewise, a dynamic load plate pressure test is known Technical test specifications for soil and rock in roadway construction, TP BF-StB, Part B, 8.3 (1997)).
Conventional measurement methods and devices separate from the compaction devices require a significant additional expense, because in addition to the compaction device measurement devices must also be made available, which generally require a correspondingly trained operator. Moreover, the number of measurements on a given surface is limited by time constraints; i.e., only some spot samples can be measured.
On the other hand, methods are also known in which special soil compaction devices are themselves used to measure, in particular, soil rigidity and/or moduli of deformation of the soil, these parameters being the central criteria for successful compaction. Such devices and methods are known for example from DE 27 10 811 C2, WO 98/17865, DE 29 42 334 C2, and EP 1 164 223 A1. Each of these publications indicates vibrating rollers that are moved over the soil that is to be compacted, and that draw conclusions concerning the soil rigidity on the basis of the vibration characteristics of the roller drum (roller tire).
As a rule, vibrating rollers are operated in such a way that the roller tires that act as the soil contact element do not lift off from the soil even when charged with vibration. As a whole, the roller tires move periodically, resulting in a relatively uniform amplitude movement of the roller tires. In contrast, the known measurement methods and devices are not suitable for other soil compaction devices, in particular vibrating plates or tampers. Vibrating plates and vibrating tampers standardly do not make contact with the soil during a significant part of a vibration-load cycle. Here, contact times have been determined that make up only about 10% of the overall vibration period. The measurement methods described above, used with vibrating rollers, are geared towards measuring signals that result from a largely constant state. Even if the roller tires jump off the soil, these airborne phases are relatively short, so that the influence of the error is low.
In contrast, in the case of tampers and vibrating plates long airborne phases and short contact times must be assumed, so that the measurement methods known from the prior art, which are geared toward a periodic movement characteristic, are not suitable. In addition, the soil contact elements of vibrating plates and tampers are subject to a rather chaotic movement characteristic, because they constantly have to absorb soil forces at different places due to the jumping or airborne phases.